Mallard v The Queen

The High Court of Australia considered an appeal by Mallard against his conviction for murder. The Attorney-General of Western Australia had referred the appellant's petition for mercy to the Court of Criminal Appeal, which subsequently refused to quash the conviction. The central dispute concerned whether the prosecution's non-disclosure of exculpatory evidence to the defence had denied the appellant a fair trial or a fair chance of acquittal.

The legal issues before the High Court included the scope of the Court of Criminal Appeal's jurisdiction on a reference under s 140(1)(a) of the Sentencing Act 1995 (WA), particularly the obligation to consider the "whole case." The court also had to determine whether the Court of Criminal Appeal had erred in refusing to consider evidence adduced on the reference, whether the jury's verdict was unreasonable or unsupportable, and ultimately, whether a substantial miscarriage of justice had occurred.

The High Court reasoned that the Court of Criminal Appeal had erred in law by failing to adequately consider the whole case, including evidence that had not been disclosed to the defence prior to or during the trial. The court emphasised the prosecution's duty to disclose material evidence, especially that which might be exculpatory or cast doubt on the credibility of prosecution witnesses, to ensure a fair trial. The court found that the non-disclosure of certain evidence, which should have been disclosed pursuant to the Statement of Prosecution Policy and Guidelines, had undermined confidence in the trial's outcome and occasioned a miscarriage of justice.

Consequently, the High Court allowed the appeal, quashed the conviction, and ordered a retrial of the appellant.